The overall purpose of the Biostatistics Core is to provide support in the areas of research design, data entry and management, statistical analysis, and presentation of results for projects and researchers in the Midwest Sexually Transmitted Infections Clinical Research Center. In addition, the Core will help with the design and sample size needs of new related STI projects and will develop new statistical methodology as the need arises. The existence of the Core assures that any unforeseen statistical analyses or design problems will immediately be brought to the attention of professionals with expertise in these areas. Details on the specific methodologies and statistical analyses for each project appear in the individual proposals.